Prediction of part geometry-dependent weld line strength in unreinforced polycarbonate

Abstract

To predict the mechanical properties of weld lines in injection-molded unreinforced amorphous plastics parts, an integrative calculation chain has been developed. Weld lines created by different flow obstacle geometries were characterized through mechanical testing. A strong dependence of the weld line strength on the geometry of the flow obstacle and the distance to the flow obstacle, which causes the weld line, was observed. Further, a dependence of the weld line strength on the loading direction was noted. These results were used to establish a simulation routine which is based on a physical description of molecular interdiffusion and uses the melt confluence angles in the weld line to determine weld line annealing behind flow obstacles. The calculated breaking stress of weld lines in polycarbonate using the model deviates on average 14% from the fracture stress that was determined experimentally.